This invention generally relates to polarographic cells which furnish a cell current. More specifically, this invention relates to such cells in which the electrodes are constantly washed by a buffer solution. Most particularly, this invention relates to an improved method and apparatus for measuring the cell current.
Plural electrode type polarographic measurement cells are known in the art. For example, such cells can be used to determine glucose content in human blood samples. The glucose content is determined by converting glucose to gluconic acid and hydrogen peroxide by reaction by an enzyme such as glucose oxidose in the presence of oxygen. Then, the hydrogen peroxide may be polarographically oxidized and the resulting current measured as being proportional to the glucose content of the sample under test.
An improved system in which the electrodes are continuously washed with a buffer solution is the subject of a co-pending U.S. Patent application. The continuous buffer wash generates a steady state current whose value may vary somewhat with time. In addition, this value must be subtracted from any peak current measured in order to obtain a true reading for the glucose concentration in any test sample. Furthermore, it would be highly desirable to make the measurement system as automatic as possible so that all an operator of the system need do is inject a sample and later read the peak current value. I have developed a measurement system which will sense the injection of a sample, hold the value of the steady state current at that time, sense the reaching of the peak current value, and subtract the steady state value from the peak value to give a true measure of the peak value. The system will give notice when a sample run is completed, and will reset itself each time a new sample is injected to allow rapid multiple sample testing. All an operator need do is inject the sample and read the peak values.